Aromatic polysulfones have excellent heat resistance and chemical resistance, and are therefore used in various applications as a material for use in molded bodies. Aromatic polysulfones are normally produced by subjecting aromatic dihalogenosulfone compounds and aromatic dihydroxy compounds to a polycondensation reaction in the co-presence of a base and a reaction solvent (see, e.g., Patent Documents 1 and 2).
The reaction mixture obtained by the above-mentioned polycondensation reaction contains aromatic polysulfones, unreacted bases, byproducts (halogenated alkalis when an alkali metal salt is used as the base), and the reaction solvent. Normally, a method is used to isolate the aromatic polysulfones from this reaction mixture, resulting in a state in which only small amounts of the unreacted bases, byproducts and reaction solvents remain.
Patent Document 3 discloses a method wherein non-solvents such as alcohol and water are used to remove byproducts and solvents from a polymer mixture, and thereafter, the bulk density of aromatic polyether polymers is increased in a mixed solvent containing an aliphatic alcohol and a ketone.
Patent Document 4 discloses a method wherein a polymer mixture is pulverized in a non-solvent, and thereafter heated under reduced pressure at a temperature lower than the glass transition temperature or the melting point of the polymer mixture and equal to or higher than the vapor pressure temperature of the reaction solvent.
Patent Document 5 discloses a method wherein a mixed solvent containing a specific solvent such as 1,3-dimethyl-2-imidazolidinone and a non-solvent of aromatic polyether polymers is added to a crude reaction solution after the removal of byproduct salts, and aromatic polyether polymers are precipitated in the non-solvent, then washed.